<?php

/**
 * Created by PhpStorm.
 * User: Administrator
 * Date: 2019/8/20
 * Time: 10:32
 */
class 使用文件缓存的例子
{

}

/**
 * Class CacheLayer
 * 在web开发中，可以通过文件缓存，大大缓解数据库的压力。 如下代码是php中使用文件缓存的例子。

CacheLayer.php
 */
class CacheLayer{
    protected $root = "";
    protected $cache = "";
    protected $key = "";
    protected $life = 0;
    public function __construct($key, $root = "/cachelayer"){
        $this->root = $_SERVER["DOCUMENT_ROOT"].$root;
        $this->key = $key;
    }
    public function expired($life_span){
        $this->life = $life_span;
        $file = $this->root."/".$this->key.".cachelayer";
        if(is_file($file)){
            $mtime = filemtime($file);
            return (time() >= ($mtime + $this->life));
        }else{
            return true;
        }
    }
    public function put($content){
        $file = $this->root."/".$this->key.".cachelayer";
        if(!is_dir(dirname($this->root))){
            return false;
        }
        $this->delete();
        $content = json_encode($content);
        return (bool)file_put_contents($file, $content);
    }
    public function get(){
        $file = $this->root."/".$this->key.".cachelayer";
        if(is_file($file)){
            return json_decode(file_get_contents($file), true);
        }
        return array();
    }
    public function delete(){
        $file = $this->root."/".$this->key.".cachelayer";
        if(is_file($file)){
            unlink($file);
            return true;
        }
        return false;
    }
}
//example.php
// Load the cachelayer and the database connection (db connection is optional)
require_once "CacheLayer.php";
require_once "db_connection.php";

// Create a instance of the cachelayer
$cl_nav = new CacheLayer("navigation");
// Check to see if the cache is expired (60 * 10 = 10 minutes)
if($cl_nav->expired(60 * 10)){
    echo "Cache doesn't exist or is expired. Rebuilding...<br />";
    // if the cache is expired rebuild it
    $result    = mysql_query("select id, title from navigation");
    $new_cache = array();
    while($row = mysql_fetch_assoc($result)){
        $new_cache[] = $row;
    }
    // Save the array into the cache
    $cl_nav->put($new_cache);
}
echo "Loading from cache...<br />";
// Get the cache
$cache = $cl_nav->get();

// Display the cache
foreach($cache as $row){
    $id    = $row["id"];
    $title = $row["title"];
    echo "<a href='/$id/$title'>$title</a><br />";
}
